1. Field of the Invention
The present invention relates to additives for lubricating oils confering antirust and antiwear effect, their method of preparation and the lubricating compositions containing the additives.
2. Description of the Prior Art
Combustibles, especially those used in fuel or heavy fuel motors contain increasingly large amounts of sulphur. At the same time, the operating conditions of these motors, defined by the compression rate and the operating temperature become increasingly stringent. In order to prevent corrosive wear by micro-seizing, the use of anti-wear lubricants able to neutralize large amounts of acids formed during combustion becomes indispensable.
The detergent and dispersant properties of a lubricant correspond to its ability to maintain in suspension the impurities and the unburned particles in the heated portions of the motor through its detergent action but also in the cold portions by its dispersant effect. The fixing of these particles in the form of varnishes or laquers is thus prevented.
The basicity reserve as well as the detergent and dispersant properties are normally conferred by overbased additives. These additives comprise alkaline-earth metal carbonates in a sulfonate, phenate or salicylate type detergent solution.
The preparation of these overbased additives is described in numerous patents.
European patent application No. 00 05357 describes a process that consists in carbonating a mixture of alkylarylsulfonate, magnesium oxide, xylene, methanol, ammonia and water.
British patent application Nos. 2,114,993 and 2,037,310, European patent application No. 0 13 807 and French Pat. No. 2,529,224 claim replacing methanol by respectively dioxolan, a mixture of ethanol and carboxylic acids, a mixture of methanol and diacetone and glycol.
French Pat. Nos. 2,445,368 and 2,454,435 describe the preparation of metallic salts of amino acids and of N-carboxyaminoacids through reaction of the acids with a basically reacting metallic compound having a basic reaction belonging to the group of the oxide or hydroxide of magnesium, of barium or of calcium, in the presence of a suspension agent soluble in the oil, such as an hydrocarbylsulfate, carboxylate, hydocarbylsuccinate of alkaline or alkaline-earth metals or an hydrocarbylsuccinimide. The reaction takes place in the presence of a hydroxylic activator such as water or an alkanol and a chalcogenic compound such as carbon dioxide.
However, although the overbased additives prevent corrosive wear due to the acids formed during combustion, they are ineffective against the abrasion provoked by the solid particles such as the unburned particles, impurities and ashes contained in the lubricant and maintained in dispersion.
In order to overcome wear, it is necessary to use antiwear additives. These additives are generally sulfur and/or phosphorus containing compounds, the most commonly used being the Zn dialkyldithiophosphates, described for example in U.S. Pat. Nos. 4,085,053; 4,094,800 and 4,101,428.